(1) Field of the Invention
The present invention relates to a method for detecting a detection site such as a notch or an orientation flat formed on a peripheral edge of a semiconductor wafer having a protective sheet joined thereto, thereby determining a handling position of the semiconductor wafer, and an apparatus using this method.
(2) Description of the Related Art
A semiconductor wafer (hereinafter, simply referred to as “wafer”) has a bottom face subjected to processing by a mechanical method such as grinding or polishing, a chemical method such as etching, and the like. Thus, the wafer is reduced in thickness. Upon performance of the processing for the wafer by these methods, a protective sheet is joined to a top face of the wafer in order to protect a wiring pattern formed on the top face of the wafer. Then, the wafer having the protective sheet joined thereto is subjected to polishing. Thereafter, when the wafer is allowed to rotate and passes between a light source and a light receiving sensor provided so as to be opposite to each other with a peripheral edge of the wafer interposed therebetween, scanning is performed on the wafer; thus, positional information about the peripheral edge is acquired. A center of the wafer is obtained from this positional information.
The center of the wafer is obtained and, concurrently, positional information about a detection site such as a notch or an orientation flat to be used for alignment is obtained. A handling position of the wafer is determined based on this positional information. More specifically, the position of the detection site is used as a reference for determination of a handling position of the wafer upon transport or determination of a handling position in consideration of a rotational direction about a center axis of the wafer when a ring-shaped frame holds the bottom face of the wafer through adhesion of a support adhesive tape (refer to, for example, JP-A 08-279547).
However, a conventional method has the following problems.
In recent years, a wafer is reduced in thickness by grinding in such a manner that an almost circular protective sheet is joined to a top face of the wafer and, then, a coating film is formed on a ground bottom face by metal deposition or the like. Herein, the protective sheet on a notch formed on the wafer is bared; therefore, the coating film is disadvantageously attached to the bared portion of the protective sheet. Further, the deposited metal is uplifted at the peripheral edge of the wafer by surface tension.
Consequently, even when the peripheral edge of the wafer is irradiated with light, transmission of the light is hindered by the coating film at the notch. Hence, the light receiving sensor, provided so as to be opposite to the light source with the wafer interposed therebetween, fails to detect the light from the light source with good accuracy, so that the position of the notch cannot be obtained.
In addition, if the bottom face of the wafer is irradiated with light and the position of the notch is detected based on intensity of the light reflected from the bottom face, scattered reflection occurs due to the metal uplifted at the peripheral edge of the wafer. Consequently, only the position of the notch cannot be identified with good accuracy.